Crystalline solar modules are made of photovoltaic cells connected in series in so-called strings. A typical solar module has 60 solar cells connected in series. These 60 cells are interconnected in three strings of 20 cells each. In today's modules, these strings are bridged in antiparallel using typically one bypass diode each. These bypass diodes have the function of conducting the electric current generated by the unshaded system past the bottleneck created by the shaded cells when one or more cells of a string are in the shade. The diodes transfer the possible electric current reduced due to the shading and conduct it past the shaded cells to thereby prevent the total electric current flow from being limited and thus the total electrical power from being withdrawn from the solar module in the event of (partial) shading. These bypass diodes are in the solar module junction box, a plastic housing in which the solar cell connections from the module are connected to flexible electric cables, which then in turn connect the solar modules to one another.
Numerous variants of the structural embodiment of the junction boxes have become known. They usually include a bottom part applied to the carrier of the solar cell array (specifically the solar module) in which the conductor elements for electrically connecting the strings and also the aforementioned bypass diodes are accommodated, and a cover placed on the bottom part, closing the junction box and protecting the electric and electronic components therein.
Current developments now point to the need for a safety shutdown of the solar modules in the event of danger, e.g., in a fire. In one case, traditional safety shutdowns are strand-based, i.e., only one electromechanical switch is used for a number of series-connected modules. Here, a dangerously high voltage may still build up due to the series connection of the modules. In another case, alternative methods make use of the module-based electronic system, which then uses electronic switches. The problem here is that there is no galvanic separation, i.e., if the electronic switch fails, the safety shutdown does not accomplish a complete disconnection, so the system still remains at risk. Other module-based approaches make use of electromechanical switches (for example, a relay) to establish galvanic separation in the event of an alarm. The problem here is that these relays consume electric current even during normal operation.